Refrigeration system with plural evaporator means

ABSTRACT

A refrigeration system particularly adapted for supermarkets and the like employing a multiplicity of refrigerated fixtures or storage rooms operating at varying load requirements wherein centrally located compressors operate all of the evaporators which may include evaporators functioning at different temperature levels from approximately freezing to substantially below freezing. The various embodiments of the refrigeration system employ a separate compressor operating at a relatively high suction pressure which produces an intermediate refrigerant evaporation temperature far below the temperature of the condensed refrigerant in the main refrigeration system and approaching the temperatures of the evaporators of the system. In each embodiment the relatively high suction pressure and intermediate temperature developed by the separate compressor is employed for reducing the temperature of the condensed refrigerant of the main refrigeration system to that intermediate temperature before supplying same to the evaporators of the refrigerated fixtures with some of the embodiments employing direct communication between the separate compressor suction and the supply of refrigerant and others employing indirect communication by heat exchanger means. The separate compressor operates at a very efficient level and thereby increases the overall efficiency and the operational characteristics of the refrigeration system.

United States Patent 11 1 Quick 1 1 Oct. 23,- 1973 REFRIGERATION SYSTEM WITH PLURAL EVAPORATOR MEANS [76] Inventor: Lester K. Quick, 45 N. Main St.,

Geln Ellyn, 111. 60137 [22] Filed: Oct. 4, 1971 [21] Appl. No.: 186,277

Related U.S. Application Data [63] Continuation-impart of Ser. No. 19,801, March 16,

1970, Pat. No. 3,645,109.

3,367,125 2/1968 McGrath 62/510 2,164,761 7/1939 Ashley 62/510 2,277,647 3/1942 Jones 62/218 2,897,659 8/1959 Wersher.... 62/510 3,427,819 2/1969 Seghetti.-.... 62/278 Primary Examiner-Meyer Perlin Attorney-Lyon & Lyon [5 7] ABSTRACT A refrigeration system particularly adapted for super- 'markets and the like employing a multiplicity of refrigerated fixtures or storage rooms operating at varying load requirements wherein centrally located compressors operate all of the evaporators which may include evaporators functioning at different temperature levels from approximately freezing to substantially below freezing. The various embodiments of the refrigeration system employ a separate compressor operating at a relatively high suction pressure which produces an intermediate refrigerant evaporation temperature far below the temperature of the condensed refrigerant in the main refrigeration system and approaching the temperatures of the evaporators of the system. lneach embodiment the relatively high suction pressure and intermediate temperature developed by the separate compressor is employed for reducing the temperature of the condensed refrigerant of the main refrigeration system to that intermediate temperature before supplying same to the evaporators of the refrigerated fixtures with some of the embodiments employing direct communication between the separate compressor suction and the supply of refrigerant and others employing indirect communication by heat exchanger means. The separate compressor operates at a very efficient level and thereby increases the overall efficiency and the operational characteristics of the refrigeration systern.

15 Claims, 5 Drawing Figures PAIENIEBumza um SBEU 3UP 4 INVENTOR. 65758 l5. 70/0:

i a fix ATTOE/WEVS mcmcam 23 m SHEET 30F 4 INVENTOR. 465766 ,5. 620/635 BY Y ATTOE/VQ S PATENTEB 001 2 3 0975 SHEET 0F 4 INVENTOR. 465765 ,6 @U/CK M om A TTOEA/ V9 REFRIGERATION SYSTEM WITH PLURAL EVAPORATOR MEANS This is a continuation-in-part of my application Ser. No. 19,801, filed Mar. 16, 1970 and entitled REFRIG- ERATION SYSTEM WITH HOT GAS DEFROST- ING, which has now issued as .U. S. Pat. No. 3,645,109.

This invention relates to refrigeration systems for operating a multiplicity of separate evaporators functioning independently to cool individual refrigerated fixtures, rooms or the like such as in supermarkets or industrial installations. The invention is directed particularly to improving the operation and efficiency of these refrigeration systems by greatly reducing the temperature of the liquid refrigerant before supplying same to the individual evaporators and accomplishing such temperature reduction in a highly efficient and totally different manner.

In recent years there has been a trend toward the use of relatively large compressors centrally located in a supermarket installation for operating the refrigerated fixtures throughout the store rather than individual compressor-fitted fixtures. This trend is similar to the concept that has been employed in industrial refrigeration for certain limited applications for many years. The plurality of evaporators for refrigerating the plurality of fixtures, rooms or the like are operated by a single compressor or plural compressors combined in parallel or compounded relationship to improve the overall efficiency and dependability of the system. Such arrangeme'nts have led to the increased use of hot gas defrostin g of the evaporators by the selection of only a portion of the evaporators for defrosting at any one time which could not be as readily and efficiently accomplished in simple systems matching a compressor to each evaporator.

While certain advantages and improved efficiencies, such as hot gas defrosting, have been employed in central refrigeration systems, there has been very little change between the basic refrigeration arrangement 40 employed in a small fixture and that used in the central systems other than the mere increase in size. This is due to thehighly variable requirements of the multiplicity of evaporators in a central system and other factors such as the variations in ambient conditions with the resultant variations in condensing pressures and temperatures, particularly when air cooled condensers are used. Conventionally the central refrigeration systems are designed to accommodate the mostadverse refrigeration load and ambient, conditions anticipated with no provisions made for affirmatively improvingsystem efficiencies under other conditions. One such design deficiency is in allowing the temperature and pressure of the condensed liquid refrigerant to vary over a substantial range which causes substantial difficulty in the functioning of the expansion valves on the evaporators due to both the variation in pressure as well as the creation of substantial quantities of flash gas in the evaporator. Moreover since the expansion valves must function properly to accommodate the worst ambient conditions when the head pressure and refrigerant temperature are very high-it is conventional to prevent the head pressure from dropping to excessively low levels in cold weather which would otherwise create an intolerable range of different pressures for the expansion valve to accommodate. Thus even the available improvement in efficiency in cold weather of allowing the head pressure to drop to low levels is sacrificed for assuring proper operation of the expansion valves and other system components.

- While it is relatively common in many systems to pro vide sub-coolers in one form or another to cool the condensed refrigerant to thereby avoid some of the flash gas created in the evaporators and thereby improve the operation of the expansion valves, the degree of cooling has been relatively minor, perhaps 10 to 15 below condensing temperature and still far above room temperature and evaporator temperature. Thus in the conventional central refrigeration system, of all of the liquid refrigerant that is conducted to each of the evaporators where it is expanded and upon evaporation is returned through the suction line to the compressor, a substantial proportion merely turns to flash gas in passing through the expansion valve thereby performing no useful work in cooling the evaporator or the fixture but merely cools the balance of the liquid refrigerant. While the proportion of flash gas will vary for the particular system and ambient conditions, in a typical system having 120F condensing temperature and 40F evaporator temperature with R-502 refrigerant there will be approximately 61 percent of the refrigerant forming flash gas in passing through the expansion valve thereby performing no useful work in cooling the evaporator. The necessity of conducting this excess liquid refrigerant to the evaporator and then returning the flash gas requires the use of larger tubing than would otherwise be necessary and in central refrigeration systems the amount of tubing used is verygreat'whereby the cost of tubing is very substantial. Moreover this flash gas must be compressed from the very low suction pressure in the evaporatonto the condensing head pressure which is a substantial pressure differential and, as

is,well.known in the art, such compression is less effi- One of the requirements in the use of hotgas defrosting with a central refrigeration system is the disposition of the refrigerantresulting from defrosting. which may be virtuallyany proportion of liquid and gas..Numerous methods have been developed to ,accomplishlthis objective-including that which is, disclosed in my copending application referred tb above.-Substantial ineffi ciencies can be introduced into the system if the method for reintroducing the defrosting refrigerant terns. On other occasions it has been necessary to replace the large compressors with even larger units and similarly increase the capacity of the condenser all of which is extremely costly. However, again it is by reason of the fact that the original compressors must handle such a large proportion of refrigerant that is merely' converted to flash gas in the evaporators that these compressors are of an insufficient capacity to accommodate additional fixtures.

Accordingly in summary the principal object of this invention is to provide an improved refrigeration system for operating a multiplicity of evaporators wherein the temperature of the liquid refrigerant supply is reduced to a temperature substantially below the room temperature by employing a separate compressor for causing such temperature reduction which compressor operates at a substantially more efficient level than the system compressors thereby improving the overall system efficiency.

Another object of this invention is to provide an improved refrigeration system with hot gas defrosting in which the resultant defrosting refrigerant is reintroduced into the liquid refrigerant supply and both sources of refrigerant are reduced to a constant temperature and pressure by the controlled evaporation through the suction of a separate compressor.

A further object of this invention is to provide a refrigeration system using piston type compressors in which the temperature of the refrigerant supply is reduced from the condensing temperature to an intermediate level between the condensing and evaporator temperatures before supplying the refrigerant to the evaporator for minimizing flash gas formed in the evaporator wherein such temperature reduction is accomplished by a separate compressor operating independently of the load requirements on the refrigeration system compressors.

Still another object of this invention is to provide an arrangement for improving the efficiency and capacity of a central refrigeration system having one or more system compressors by means of employing a separate compressor to cause a substantial reduction in the temperature of the liquid refrigerant subsequent to condensing but prior to supplying same to the evaporators.

A still further object of this invention is to provide an improved central refrigeration system operating evaporators at two or more suction and temperature levels wherein separate compressor means are employed to reduce the-temperature of the liquid refrigerant being supplied to the evaporators to temperature levels more closely approximating the respective temperature levels of the evaporators whereby flash gas formed in each evaporator is minimized.

Still another object of this invention is to provide a refrigeration system operating evaporators at two or more temperature and suction levels in which the compressors are compounded with an intercoolerbetween the compounded stages modified to provide a supply of liquid refrigerant for the lower of those two stages at a temperature more closely approximating the temperature of the evaporators of such lower stage and wherein a separate compressor is employed for reducing the temperature of the refrigerant supply for the highest temperature evaporators.

Another object of this invention is to provide a novel central refrigeration system wherein the normal liquid supply is greatly reduced in pressure and temperature at the location of the compressors with the flash gas produced by such reduction being directly and efficiently returned to such compressors. A further object is to provide such a system wherein the lengthy refrigerant supply and suction lines to the remotely located fixtures may be reduced in size by reason of such direct flash gas return. Still another object is to provide such a system wherein the pressure in the liquid refrigerant supply line to the evaporators is regulated to a substantially constant level far below the high head pressure on the compressors whereby a pressure differential incentive for the return of condensate from hot gas defrosting is always present in the liquid refrigerant supply side of the cycle. Still another object is to provide such a refrigeration system in which means are provided for regulating the pressure of the hot gaseous defrosting refrigerant to a constant level whereby the pressure differential across the evaporators is always a predetermined amount thereby permitting accurately predictable defrosting times for respective evaporators. A still further object is to provide such a system wherein the flash gas is returned to one or more compressors operating at the higher suction pressures thereby improving the efficiencies of all of the compressors operating at lower suction pressures.

Other and more detailed objects and advantages of this invention will appear from the accompanying description and drawings wherein:

FIG. 1 is a schematic illustration of the preferred form of my invention illustrating a central refrigeration system employing compressors in compounded relationship operating fixture evaporators at three different suction pressures and a separate compressor operating at a high suction pressure to reduce the temperature of the liquid refrigerant supply to substantially below room temperature as well as accommodating the gaseous refrigerant returned from the hot gas defrosting.

FIG. 2 is a schematic illustration of a modified form of the refrigeration system of FIG. 1 in which a total of three separate compressors are employed for reducing the temperature and pressure of the liquid refrigerant supply for the three separate temperature levels of evaporators. 7

FIG. 3 is a schematic illustration of the refrigeration system of this invention operating evaporators at two different temperature and suction levels having the compressors compounded with the intercooler therebetween providing the source of liquid refrigerant for the low temperature evaporator and a separate compressor reducing the pressure and the temperature of the liquid supply to the high temperature evaporators as well as the intercooler.

FIG. 4 is a schematic illustration of another modified form of. refrigeration system of my invention wherein the liquid refrigerant for two completely separate refrigeration systems, as for example for different temperatures, is reduced to an extremely low temperature by still another completely separate refrigeration system employing a separate compressor. I

FIG. 5 is a schematic illustration of another modified form of refrigeration system of my invention in which the liquid refrigerant for the system evaporators is reduced in a somewhat conventional sub-cooler with the suction of the sub-cooler connected to a separate compressor.

While the various figures illustrate varying numbers of system compressors for operating the evaporators it will be understood and readily appear to those skilled in the art that more or fewer system compressors may be used in any of the systems depending on the load requirements and other factors. However with respect to the separate compressors for reducing the temperature and sometimes the pressure of the liquid refrigerant for the overall system, it is intended and will be understood that only the actual compressors illustrated and described are employed and in each instance these are substantially smaller in their capacity and power requirement than the remaining compressors of the system. In some instances the separate compressor may be a separate portion of a larger compressor by using special heads but the operation thereof will remain the same as though it were physically separate. Furthermore while the evaporators are illustrated in varying numbers and detail in the five systems illustrated by the figures, it is to be understood and will readily appear to those skilled in the art that normally a great many evaporators will be provided and operating at each temperature level with the exact number being dependent on the-size of the supermarket or industrial installation.

While only FIG. 1 includes an illustration of the appropriate components for accomplishing hot gas defrosting of the various evaporators, it will be understood and readily appear to those skilled in the art that the systems of FIGS. 2 through 5 may be provided with the appropriate components for accomplishing hot gas defrosting and that such has been omitted from these Figures merely for simplicity of illustration. Finally with respect to the versatility and adaptability ofthe compressors of the refrigeration system of this invention, the term compressors" shall mean piston type compressors that are common in the industry rather' tem as to other types of installations will readily appear to those skilled in the art. In the usual supermarket there are at least three distinct levels of refrigerated fixture temperatures required which are normally referred to as standard temperature fixtures (i.e. diary, produce and fresh meat), low temperature fixtures (i.e. frozen foods and walk-in freezers) and ultra-low temperature fixtures, (i.e. ic ecream cases and special frozen food fixtures requiring very low back pressures). To provide these three temperature levels in a supermarket or any installation having similar requirements, it is necessary to provide compressors operating at three distinct suction pressures, if the best operating efficiency is to be maintained, which'compressors are commonly referred to by the corresponding temperature level of the fixtures to which their suctions are connected. Thus in FIG. 1 there are two compressors and 1 1 connected in parallel to operate the standard temperature fixtures and will be referred to as the standard temperature compressors. Two more compressors l2 and 13 are connected in parallel to operate the low temperature fixtures and compressor 14 is the ultra-low temperature compressor.

In their normal refrigeration operation compressors 10, 11, 12, 13 and 14 are compounded in this illustrated system of FIG. 1. The discharge 16 of ultra-low temperature compressor 14 is connected through conduit 17 to the suction side 18 of the low temperature compressors 12 and 13. The discharge sides 19 of low temperature compressors 12 and 13 are connected through conduit 20 to the suction side 21 of standard temperature compressors l0 and 11. The discharges 22 of standard temperature compressors 10 and 11 are separately connected to a discharge accumulator and oil separator 23 which has an outlet stand pipe 24 connected to a conduit 25 leading to the system condenser 26 and thence through a high side float valve 27 to the system receiver 28. As is well known to those skilled in the art, the high side float valve 27 functions to allow only liquid refrigerant to flow from the condenser 26 to the receiver 28 without regard for temperatures, pressures, rate of supply, etc. and the particular importance of the high side float valve in this system will be described hereinafter. As thus far described it may be seen that the entire system has a single condenserreceiver arrangement for supplying the liquid refrigerant requirement of all of the evaporators rather than providing separate condenser-receivers for each of the temperature levels. The ultra-low temperature com- 'pressor 14 is compounded with the low temperature compressors 12 and 13 which are in turn compounded with the standard temperature compressors l0 and 1 1.

The above-mentioned discharge accumulator and oil separator 23 forms no part of the invention of this application although it will be understood that some form of oil separation and return must be provided in the refrigeration system of this type. The arrangement illustrated in FIG. 1, as well as FIG. 2, is of the type more fully'disclosed in my copending application Ser. No. 8 15,452 entitled Refrigeration System Oil Separator but will be briefly described here for completeness. The vessel comprising the discharge accumulator and oil separator 23 serves to separate the oil from gaseous refrigerant discharged from the compressors and to maintain an oil supply 33 in the bottom of the vessel. An oil line 34 is connected through a header to individual conduits returning to the crank cases of each of the compressors 10 through 14. Each such oil return conduit has a separate valve 35 the operation of which is individually controlled by a float actuated sensor'36 associated with the compressor to which the oil return lineand valve are connected'Thus as the sensor 36 associated with a compressors enses a drop in the desired oil level in the compressorv the associatedvalve. is

opened to cause the return of oil to that compressor by virtue of the higher pressure existing in the vessel of separator 23 whereby the desired oil levels in each of the compressors are independentlymaintained.

Returning to the description of the closedcycle refrigeration system of FIG. 1, the receiver 28.i s connected through a conduit 40 to a liquid refrigerant header 42, all of which is situated at the central location of the compressors. The liquid header 42 is connected through conduits 43 to the evaporators 44 of the-refrigerated fixtures. For simplicity of illustration only one evaporator 44 and six branch conduits 43 are shown although one or more separate evaporators will be associated with each conduit 43 and in most commercial installations of this type there will be a great many more than six branch conduits 43.

As is conventional, each evaporator 44 is provided with an expansion valve 45 and a by-pass line 46 having a check valve is provided for purposes of by-passing the expansion valve 45 during hot gas defrosting in which the refrigerant flows in the reverse direction. In addition each evaporator will be provided with a temperature responsive control such as a conventional liquid line solenoid valve or, as shown in each of the drawings, a suction pressure regulator valve 47.

Each evaporator is connected through a suction conduit 48 to a suction header through, for purposes of hot gas defrosting, a three-way valve 49. The three-way valve 49 is operable to selectively connect the suction line 48 to either the common hot gas header 50 or one of the three respective suction headers 51, 52 or 53. It is to be noted that as viewed in FIG. 1 the two suction conduits 48 toward the right hand side are connected through three-way valves to the standard temperature suction header 51 whereby the associated fixtures would be standard temperature fixtures, the two middle suction conduits 48 are connected through three-way valves to the low temperature suction header 52 whereby the associated fixtures would be low temperature fixtures, and the two left hand suction conduits 48 are connected through three-way valves to the ultralow temperature suction header 53 whereby the fixtures associated with those two suction conduits would be ultra-low temperature fixtures. The standard temperature suction header 51 is connected through conduit 54 to the suction side 21 of compressors and 11. The low temperature suction header 52 is connected through conduit 55 to the suction side 18 of low temperature compressors 12 and 13. The ultra-low temperature suction header 53 is connected through conduit 56 to the suction side of compressor 14.

A by-pass line 57 with a check valve 58 is connected from the ultra-low temperature suction line 56 to the discharge side 16 of the ultra-low temperature compressor 14 for allowing the by-pass of refrigerant upon the failure of compressor 14 or the temporary return of an excess quantity of refrigerant to compressor 14. In essence the suction from all of the ultra-low temperature fixtures will then be connected to the suction side 18 of the low temperature compressors l2 and 13 until the malfunction of compressor 14 is corrected or the excessreturn load is reduced. While the suction provided by low temperature compressors 12 and 13 will not be as low as desired for maintaining the ultra-low temperature in these fixtures the temperature maintained will be adequate for a short duration.

Thusit will be seen that during the normal refrigerating operation of a given evaporator 44 the associated three-way valve 49 is positioned to connect the suction conduit 48 to the associated suction header (51, 52 or 53) to return the evaporated refrigerant to the appropriate compressor whereby the appropriate suction pressure is maintained on that evaporator for providing the desired temperature and yet the liquid refrigerant is supplied to all of the evaporators from thecommon liquid header 42.

In order to accomplish hot gas defrosting of the evap-' orators in the system of FIG. 1 as thus far described, a variety of arrangements may be used but I have illustrated a still further improvement in my invention of a refrigeration system adapted for hot gas defrosting similar to that described in my aforementioned parent application Ser. No. 19,801, now U. S. Pat. No.

3,645,109, entitled Refrigeration System With Hot Gas Defrosting," which application is directed specifically to the improvements in hot gas defrosting. When it is desired to defrost a given evaporator 44 the associated three-way valve 49 is repositioned from its normal refrigerating connection wherein the suction conduit 48 is connected to the suction header (51, 52 or 53) to the position wherein the suction conduit 48 is connected to the hot gas header 50. Simultaneously a solenoid valve 64 in conduit 20 is closed thereby eliminating the connection of the discharge sides 19 of low temperature compressors 12 and 13 to the suction side 21 of standard temperature compressors 10 and 11. A conduit 65 connects the discharge sides 19 of low temperature compressors 12 and 13 to hot gas header 50 to supply the hot gaseous refrigerant for defrosting from compressors 12 and 13. A pressure regulating valve 66 is provided in conduit 65 and functions to limit the pressure in conduit 65 to a predetermined constant downstream pressure of a relatively high level which is related to the temperature of gas desired to accomplishing the defrosting. In order to avoid the occurrence of excessive pressures on the discharge sides of compressors 12 and 13, as might be produced by the throttling or pressure regulating effect of valve 66, a by-pass conduit 67 is connected from the compressor discharge side 19 to the accumulator and oil separator vessel 23. A pressure regulating valve 68 of the type for regulating upstream pressure is provided in by-pass conduit 67 and is set for a slightly higher pressure value than the setting of valve 66 whereby any excess refrigerant not being passed through valve 66 for hot gas defrosting purposes will be discharged throughby-pass conduit 67 into the vessel 23 thereby entering the normal refrigeration cycle. A check valve 69 is provided in by-pass conduit 67 to prevent reverse flow therethrough such as would otherwise occur during normal refrigeration operation ofthe system (when there is no hot gas defrosting being performed) wherein valve 64 would be open and the pressure on the discharge sides 19 of compressors 12 and 13 would be substantially lower than the pressure in vessel 23. By this arrangement it may be seen that defrosting gaseous refrigerant is provided at a precisely controlled and constant pressure without regard for load fluctuations or ambient conditions. If in a given installation a greater heat load capacity for defrosting is desired the valving, can be rearranged to take the defrost gaseous refrigerant from the main discharge line 25 with an appropriate throttling valve for assuring the proper pressure in low ambient conditions.

In connection with the hot gas defrosting arrangement, at desuperheater 70 is provided in heat exchange relationship with conduit 65 between the pressure regulator valve 66 and the hot gas header 50 for eliminating at least most of the superheat in thegaseous refrig erant whereby the refrigerant will be more nearly. its saturation temperature for that predetermined pressure as regulated by valve 66. This avoids excessive heating of the conduits leading to the evaporators which has been found advantageous without adversely effecting the defrosting. Desuperheater 70 is shown as a watercooled type with the water flowing therethrough as controlled by valve 71 which is in turn controlled by'a temperature responsive sensor 72 associated with'the conduit 65 downstream of the desuperheater. In this manner the temperature of the hot gas may be lowered to approximately the saturation temperature for the pressure setting of regulator valve 66. It will be obvious to those skilled in the art that any form of desuperheater may be used for accomplishing this objective.

The desuperheated gaseous refrigerant passes from hot gas header 50 through the three-way valve or valves 49 associated with the evaporators to be defrosted, then passes in a reverse direction through the suction conduit 48 to the evaporator 44, and thence through the by-pass conduit 46 into the liquid line 43. A check valve 73 is provided in each liquid line 43 to prevent the flow of the defrosting refrigerant into the liquid header 42. A branch conduit 74 connects each liquid line from a point between the evaporator and the check valve 73 to a condensate header 75 for conducting the defrosting refrigerant from line 43 to header 75. Each branch conduit 74 is provided with a check valve 76 to preclude the reverse flow of defrosting refrigerant from header 75 into the liquid line 43 of any of the other evaporators operating in its normal refrigerating cycle which reverse flow would otherwise occur due to the pressure differentials as will hereinafter appear more fully. A conduit 77 having a pressure regulating valve 78 connects the condensate header 75 to the receiver 28 which, as hereinafter described, is maintained at a low pressure whereby the defrosting refrigerant will be returned directly to the refrigerating cycle regardless of its gaseous or liquidstate. Valve 78 functions to maintain a constant upstream pressure (i.e. header 75) when it is desirable to maintain a higher pressure in the suction header than is maintainedin the receiver 28 and liquid header 42. For example this higher pressure in condensate header 75 precludes the flow of liquid refrigerant into header 75 from one of the liquid lines 43 during normal refrigerating operation. However it has been found to be advantageousin many installations to provide appropriate valving between the liquid lines 43 and the header 75 and to simply allow the pressure in header 75 to drop to the pressure maintained in receiver 28 by eliminating the regulating valve 78. By such arrangement, a very'high pressure differential is created between the hot gas header 50 and header 75 thereby maximizing the rate of defrosting refrigerant flow through the evaporator to minimize the time required for accomplishing a complete defrost of the evaporator coils and related components such as fixture drip pans. Of course it is quite common for significant quantities of gaseous refrigerant to be returned with the defrosting refrigerant after passing through the evaporators to be defrosted and this is particularly true.

during the final stages of defrosting and with this high pressure differential. In the system of FIG. 1 this gaseous refrigerant will be returned to the receiver 28' where, as hereafter described, it will be disposed of rather than reintroducing such gaseous refrigerant into the liquid refrigerant being supplied to an evaporatorv where it can cause substantial malfunctioning in. the normal refrigeration operation. In another operable arrangement a high side float valve is substituted for regulating valve 78 whereby the liquid defrosting refrigerant is allowed to return to receiver 28 rapidly at a low pressure but as gas starts to return the flow is restricted thereby raising pressure and temperature for the final stages of defrosting.

Referring again to the liquid refrigerant supply portion of the refrigeration system, the receiver 28 continually maintains a volume of liquid refrigerant adequate to meet the varying needs of the multiplicity of evaporators employed in this type of system as contrasted with a simple single evaporator system wherein a critical charge of refrigerant is provided in the system with no vessel corresponding to receiver 28 being required. As previously mentioned, the high side float valve 27 serves to feed only liquid refrigerant from the condenser 26 to the receiver 28 without regard for the pressure or level of refrigerant in receiver 28. In accordance with this invention means are provided for continually evacuating receiver 28 to a predetermined reduced pressure and temperature and these means may include a suction conduit 80 connected from the top of receiver 28 to the suction of a separate compressor 81 with a pressure regulating valve 82 provided in conduit 80. Valve 82 is of the type commonly known as an evaporator pressure regulating valve for controlling the upstream pressure, that is, the pressure in receiver 28 to a precise predetermined value. Compressor 81 operates continuously to evacuate gas from receiver 28 as required to maintain the pressure value as regulated by EPR valve 82 and, obviously, this gas evacuation causes a reduction in the temperature of the'refrigerant remaining in receiver28. The discharge of compressor 81 is connected through conduit 83 to the accumulator oil separator 23 with acheck valve 84 provided in conduit 83 to preclude reverse flow. Compressor 81 is relatively small compared to the system compressors 10 through 14 and is adapted to operate continuously. Compressor 81 is provided with the same type of oil return fromseparator 23 as heretofore described comprising an oil level sensor 36 operating a valve 35 to supply oil asrequired. Since compressor 81 is operating continuously and yet the suction load of evacuating gas from receiver 28 to the desired predeterminedpressure may drop below the capacity of compressor 81, as for example in low ambient conditions wherein the condensing pressure and temperature will be verylow, I prefer to'provide a suction conduit 85 with a check valve 86 connecting the suction of compressor 81 to the the suction conduit 54 leading to the suction side of the standard temperature compressors 10 and 11. In this manner the capacity of compressor 81 may be employed continuously in a useful manner, whether partially in evacuating receiver 28 and. partially assisting the standard temperature compressors or totally in evacuating receiver 28.

The load on compressor 81 from the evacuation. of receiver 28 will becomprised of theflash gas created by the liquid refrigerant passing from the high condensing pressure in condenser 26 through high side float 27 to the lower receiver pressure and the gaseous refrigerant returning from defrosting through conduit 77'. If the pressure regulating valve 78 is employed in'conduit 77 to maintain a higher'pressure in header th'an in receiver 28 then the defrosting refrigerant may include some flash gas as caused by the pressure reduction through valve 78 as well as the usual quantity of gaseous refrigerant that is not condensed in passing through the evaporator, particularly in the final stages of defrosting.

The specific pressure and'ternperature maintained in receiver 28 may be established at different levels for different refrigeration systems depending on the requirements of the particular system but my invention contemplates that the temperature will be set at a level substantially midway between the evaporator temperature and the normal condensing temperature. However, when there are multiple evaporators operating at different temperatures from one receiver (as here) an average or compromise temperature is selected. Thus for example, without limiting this invention, a typical condensing temperature using an air cooled condenser may be 120F and I prefer maintaining receiver 28 at a temperature of 52F with the warmest evaporator temperature being perhaps to F, and the coldest evaporator temperature being perhaps 40F. While it is not uncommon for refrigeration systems to be provided with some form of liquid sub-cooling to reduce the temperature below the condensing temperature, this reduction is normally in the range of 10 to 15 which is all that is possible whereas in my system a temperature reduction of 70 or 80 or perhaps more is accomplished. While this desired reduction in temperature creates flash gas in receiver 28 due to the reduction in pressure, it likewise eliminates the creation of this same quantity of flash gas at the evaporator. As is well known flash gas is created at the expansion valve of the evaporator in every refrigeration system since the pressure is reduced from the liquid line pressure to the evaporator pressure and this evaporation into flash gas serves to lower the temperature of the reamining liquid from the liquid line temperature to the evaporator temperature. The quantity of flash gas created actually will depend on this temperature differential rather than the pressure differential. It is to be noted that such flash gas produces no useful work in the evaporator but rather is detrimental to the operation of the evaporator and in the cooling of the refrigerated fixture although the flash gas obviously would represent part of the load on the system compressors 10 through 14 since it must be returned and recompressed. Of course the flash gas also represents part of the volume that must be conducted by the suction conduits and, in its liquid form, part of the liquid volume that must be conducted by the liquid supply lines whereby such piping must be sized to accommodate those volumes. However any portion of the flash gas usually produced at the expansion valve that can be eliminated upstream thereof will allow a corresponding reduction in the necessary size of the liquid supply lines and suction lines and a resultant reduction in cost of installation.

However in addition to the foregoing benefits of this arrangement an even more significant improvement in the refrigeration system is in the improvement of the overall efficiency. The recompression by compressor 81 of the flash gas created in receiver 28 by reason of the pressure reduction from the condensing pressure is performed at a smaller pressure differential and with a much higher suction pressure than when the flash gas is created in the evaporators. The efficiency of the compression of gaseous refrigerant depends on the actual pressure of the refrigerant in that the higher the pressure the larger the quantity by weight of refrigerant that will be compressed in each cycle of th compressor. Thus compressor 81 is operated at a highly efficient level far above the level of a compressor in any conventional refrigeration system and far above that of compressors' 10 through 14 of the system of FIG. 1. The magnitude of the increase in efficiency of the overall system will depend on many factors and an example will be given hereinafter.

In the installation and operation of a refrigeration system as shown in FIG. 1 a variety of different pressure settings may be selected for the various regulating valves 66, 68, 78, and 82 depending on a number of factors such as the particular refrigerant selected and the common ambient conditions encountered. For purposes of illustration and without limiting the scope of this invention, the system of FIG. 1 will now be de scribed in connection with typical pressure settings that might be selected when using refrigerant R-502 in a supermarket refrigeration system. The pressure regulating valve 82 may be set for 100 psi with a resultant temperature of the liquid refrigerant in the receiver 28 of approximately 52F. A desirable setting of the hot gas defrosting pressure regulating valve 66 might be 215 psi whereby the defrosting gaseous refrigerant, after desuperheating by desuperheater 70, would be slightly over 100F, perhaps 110F to avoid any actual condensing by desuperheater 70. In turn the regulating valve 68 would be set a few pounds higher than valve 66, perhaps 218 psi. Finally if the regulating valve 78 for controlling the pressure in condensate 75 is desired, for the reasons discussed above, it might be set to maintain a pressure of perhaps 185 psi whereby a constant pressure differential of 30 psi is created between hot gas header and condensate header 75 for causing the flow of defrosting refrigerant through the evaporators. Of course if valve 78 were eliminated as discussed above, the pressure in condensate header 75 would be allowed to drop to 100 psi (the pressure in receiver 28) whereby the pressure differential would be 115 psi. In either case this predetermined pressure differential results in a predictable and consistent defrosting refrigerant flow through the evaporators whereby an appropriate defrosting time may be selected for each evaporator and a consistent defrosting will result under all ambient conditions although it willbe appreciated that the time duration for defrosting a given evaporator will be reduced in relation to the magnitude of the pressure differential established between headers 50 and 75. In a supermarket installation of this a typical suction pressures on'the three levels of compressors for this arangement mightbe as follows: 41 psig on standard temperature compressors 10 and ll, 12 psig on low temperature compressors 12 and 13 and 0 psig on the ultra-low temperature compressor 14.

Thus it may be seen that in the system of FIG. 1 the liquid refrigerant will be at a constant temperature and the pressure differential across the expansion valve 45 of a given evaporator will be substantially constant under all ambient conditions, which pressure differential will be approximately 59 psi for the standard temperature evaporators, 88 psi for the low temperature evaporators and psi for the ultra-low temperature evaporators. As will readily appear to those skilled in the art this will improve the ability to select and properly set the expansion'valves and will greatly improve their performance. The quantity of flash gas produced in each evaporator is substantially reduced by this system over that which would occur in a conventional system. Of course the proportion of flash gas created in an evaporator will vary depending on the pressure main-' tained in the evaporator due to the pressure differential between the and psig liquid refrigerant pressure an the evaporator pressure. Moreover by providing this constant and relatively low liquid refrigerant supply pressure in receiver 28 it is possible to permit the condensing or head pressure of the system to vary over a much wider range as dictated by ambient conditions including permitting the pressure to drop to otherwise unacceptably low pressures which results in a substantial reduction in the power consumption of the compressors. Of course the improved efficiency of the overall system obviously permits the selection of system compressors of smaller sizes at lower prices when a system of this type is designed and such reductions in sizes and prices far exceeds the size and price of compressor 81.

As an example of the improved efficiency and reduced compressor capacity required for the system of FIG. 1, is a typical installation in a supermarket using the six compressors illustrated in FIG. 1 and substantially the requirements set forth in the preceding paragraph there was an actual compressor power requirement of approximately 57 horsepower. The substantially identical refrigeration system employing only compressors through 14 and omitting the receiver pump out compressor 81 required approximately 80 horsepower for the compressors. In still another competing refrigeration system employing separate refrigeration cycles for the three different temperature levels 140 horspower was required to refrigerate the same fixtures in the same store and such competing system is highly respected and accepted in the industry as being.

relatively efficient. Comparing the efficiencies of the systems by comparing the quantity of refrigeration produced or the power consumed, under the same high condensing temperature conditions the system of FIG. 1 in this installation produced 7.3 'btus per watt while such competing system produced only 3.9 btus per watt. Moreover an increased efficiency in produced refrigeration per unit of power of up to 30 percent will occur under low ambient conditions whereby low condensing temperatures may be used with the system of FIG. 1, which increase is not possible with such com- I peting system or any others in which the head pressure must be maintained at elevated levels.

Referring now to FIG. 2 a modified form of the refrigeration'system of FIG. 1 is illustrated with many of the components remaining the same or substantially so and being more fully disclosed in the description of FIG. 1. To the extent that the components of FIG. 2 correspond to or are substitutes for the like components of the system of FIG. 1,.a like numeral in the 100 serieswill be employed and the description here of that component will be minimized. It is to be noted that the system of FIG.2 does not include the element for accomplishing hot gas defrosting of the evaporators but it will readily appear to those skilled in the art that the defrosting .arrangementof FIG. 1 or any comparable arrangement may and would normally be employed therein. Compressors 110 and 111 are the standard temperature compressors having their discharges 122 connected to the accumulator and oil separator 123 with their suctionsides 121 connected to both the suction conduit 154 from the evaporators and the conduit 120 connected to the discharge sides 119 of the-low temperature compressors 112 and 113. Again an ultralow temperature compressor 114 has its discharge 116 connected through conduit 117 to the suction sides 1 18 of the low temperature compressors 112 and 113. The suction side of ultra-low temperature compressor 114 is connected through conduit 156 to suction header 153. The suction side of low temperature compressors 112 and 113 is connected through conduit 155 to low temperature suction header 152. Conduit 154 is con- 14 ture compressors to the suction header 151 for the standard temperature evaporators. The evaporators 144 and the associated controls remain the same as described with respect to FIG. 1. The system compressors are compounded with the entire discharge passing into the vessel of. separator 123 and out through the standpipe 124, through conduit 125 to condenser 126 and then to receiver 128.

. In this embodiment of FIG. 2, receiver 128 remains at condenser head pressure and the liquid refrigerant is supplied through conduit to a pressure regulating valve 141A which functions to maintain a reduced and constant downstream pressure. Valve 141A is of the i type commonly known in the industry as a crank case pressure regulator or CPR valve. The predetermined pressure maintained by valve 141A is selected to be lower than the lowest condensing or head pressure permitted by the system condenser and its controls under the most extreme conditions and yet higher than the highest evaporator suction pressure such as produced by standard temperature compressors 110 and 111. In a typical supermarket installation this valve 141A may be set to maintain a downstream pressure of 100 psi with a resultant liquid temperature of 52F, the same as maintained in receiver 28 of the system of FIG. 1. The reduction in pressure by valve 141A will produce flash gas in the manner heretofore described and therefore a separating vessel or chamber A is provided immediately downstream of the valve for allowing the gaseous and liquid refrigerant to separate. The flash gasis removed through a conduit'161A connected to the suction side of a small separate compressor 181A similar in its function to compressor 81 of the system of FIG; IQMeans are provided for controlling the removalof the flash gas through conduit 161A to avoid either the excess accumulation of flash gas in chamber 160A or the inadvertent return of liquid refrigerant to the suction of compressor 181A and, as shown in the drawings, these means may include a float control 162A provided in the chamber 160A and connected -'to and controlling the operation of a valve 163A in conduit 161A. The controlled operation of valve 163A by float control 162A may be either an on-off switching betially filled with liquid refrigerant unless there simplyis nected from the suction sides of the standard temperano additional liquid refrigerant available fromv receiver 128. Thus it may be seen that the pressure and temperature reduction of the liquid refrigerant by'the regulating valve 141A form the pressure and temperature in receiver128 to the desired lower level is accomplished automatically andv continually without employing a subcooler or the like and yet the resultant flash gas is im mediately removed and returned directlyto the refrigeration system by compressor 181A which has its dis charge connected through conduit 183 to the oil separator 123. A header 142A is connected to'chamber 160A and serves as a refrigerant supply for the standard temperature evaporators. I

A second pressure regulating valve or CPR-valv 1418 is provided in a conduit connecting header-142A to a second chamber 1608 for reducing the pressure and temperature of the liquid refrigerant from the values existing in header 142Ato a temperature more closely approaching the temperatures maintained in the low temperatures evaporators as for example the temperature of perhaps, 16F. Chamber 1603 has a conduit 161B connected to another small separate compressor 181B with the valve 163B and float control 1628 for evacuating the flash gas created in the pressure reduction through valve 141B and maintaining the reduced pressure and temperature. The discharge of compressor 181B is connected through a conduit 1838 to conduit 183 thereby returning the refrigerant to the normal cycle. The bottom of chamber 160B is connected to a liquid header 1428 for supplying liquid refrigerant to the low temperature evaporators at this further reduced temperature. Similarly another CPR valve 141C is provided for reducing the pressure of the liquid refrigerant from header 142B into a chamber 160C and thence to a liquid header 142C for supplying the refrigerant to the ultra-low temperature evaporators. Again the magnitude of the pressure and temperature reduction may be any amount desired but ideally it will approach a temperature reduction of one-half the difference between the upstream refrigerant temperature and the evaporator temperatures thereby again maximizing the efficiency of this reduction while minimizing the flash gas formed in the evaporators. A third separate compressor 181C may be provided with its suction conduit 161C connected through valve 163C to the chamber 160C with the valve being operated by control 162C. The discharge of compressor 181C is connected through conduit 183C either directlyor indirectly (as illustrated) to the oil separator 123 for returning the refrigerant to the normal cycle.

The series of reductions in pressure and temperature are illustrated in FIG. 2 as an example of the manner in which this invention may be employed to maximize efficiency in systems employing multiple evaporators operating at plural temperature and suction levels but it will be appreciated by those skilled in the art thatin many smaller installations the gain in efficiency at each succeeding level may be sufficiently small as to render unwarranted the provision of the additional equipment. Moreover it will also appear to those skilled in the art that one or more of the successive pressure and temperature reductions, particularly at the lower levels, may approximate the suction pressure maintained by one of the system compressors whereby the suction line 161 of the particular separation chamber 160 may be connected to the suction of a system compressor to accomplish the improved efficiency without the need for an additional compressor at that level. It should be noted that FIG. 2 also illustrates the provision of the oil return system described with respect to FIG. 1 for each of the eight compressors illustrated in FIG. 2 by means of the same individual float controls 136 and valves 135.

Referring now to FIG. 3, another modified form of the system of this invention is illustrated in a greatly simplified form although it will be understood and readily appear to those skilled in the art that the variety of additional components described with respect to FIGS. 1 and 2 normally would be included in the system of FIG. 3, such as the means for oil return to the compressors and for hot gas defrosting. Again insofar as the components of this system correspond directly to the components of the systems of FIGS. 1 and 2, nu-

merals in'the 200 series will be employed for simplicity of description and correlation. Compressors 210 and 211 are the standard temperature compressors having their suction sides 221 connected through a conduit 254 to the suction h'eader 251 that is connected to the standard temperature evaporators 244, only two of which are illustrated although a multiplicity thereof will normally be provided. A conduit 220 also connects the suction sides 221 of the standard temperature compressors to a vessel 285 which serves the function, among other things hereinafter described, of a flash type inner-cooler as is well known in the art. The low temperature compressors 212 and 213 have their discharges 219 connected to the vessel 285, preferably discharging the gaseous refrigerant into the lower portion of the vessel for bubbling through the liquid refrigerant present thereby reducing the temperature of the discharge gas. The suction sides 218 of the low temperature compressors are connected through a conduit 255 to the low temperature suction header 252 which is connected to the low temperature evaporators 244 illustrated in the left hand portion of the Figure.

Thus again in the system of FIG. 3 the compressors are arranged in compounded relationship and if ultralow temperature evaporators are included then the compressor therefor may be compounded in the manner illustrated in FIGS. 1 and 2. Standard temperature compressors 210 and 21 1 discharge the compressed re- 1 frigerant to condenser 226 and the condensed refrigerant flows through the high side float valve 227 to receiver 228 in the manner described with respect to FIG. 1. As in the system of FIG. 1, a separate compressor 281 continually draws a suction on receiver 228 through conduit 280 with the suction pressure being controlled by the EPR valve 282 whereby a constant pressure is maintained in the receiver, as for example 100 psig and 52F for refrigerant 502. The discharge from separate compressor 281 is combined with the discharge from the standard compressors supplied to the condenser 226. Again I prefer to provide a conduit 285 having a check valve 286 connected between the suction sides of the standard temperature compressors and separate compressor 281 for the latter to assist the former when the load of evacuating the receiver 282 is below the capacity of compressor 281. The liquid refrigerant for the standard temperature evaporators (illustrated on the right hand side of FIG. 3) is supplied directly to those; evaporators from receiver 228 through conduit 240 and header 242 in the manner illustrated and described withrespect to FIG. 1. However the liquid refrigerant supply for the low temperature evaporators is supplied from the inter-cooler vessel 285 through conduit 240A and header and header 242A at a temperature-and pressure as maintained in vessel 285 by thestandard temperature compressors 210 and 211 and in the context of the heretofore described systems, this' temperature may be approximately 10F. Thus it will be seen that very little flash gas will be created in the expansion of refrigerant into the low temperature evaporators thereby minimizing the inefficiencies and problems heretofore discussed. The supply of liquid refrigerant for vessel 285 is provided through conduit 286 from receiver 228 through a float valve assembly 287 whereby an adequate supply of liquid refrigerant is maintained at all times in vessel 285 which thereby serves as a receiver forsupplying the multiplicity of low temperature evaporators to accommodate their fluctuating loads. The float valve assembly may be of any convenient type such as a float sensor 288 operating a valve 289 to admit liquid refrigerant as needed to maintain the desired refrigerant level. The system of FIG. 2 provides the basic efficiencies described with respect to FIG. 1 but adds the additional efficiencies and advantages with respect to supply refrigerant of an even further reduced temperature to the low temperature evaporators similar to that which is provided by the system of FIG. 2 but by merely employing the suction of the standard temperature compressors rather than a second separate compressor.

In FIG. 4 another modified form of the system of this invention is illustrated in a greatly simplified form and again insofar as the components of this system correspond to those of the preceding Figures numerals in the 300 series will be employed. The system of FIG. 4 combines three completely separate, closed cycle, refrigeration systems which may comprise the standard temperature system, the low temperature system and the refrigeration system accomplishing the invention hereof. It will be understood and readily appreciated by those skilled in the art that this concept may be applied to more than the two fixture refrigerating systems illustrated and that such plural systems need not be operated' at different temperature levels. The discharge from the standard temperature compressor is supplied to a condenser 326A, receiver 328A and thence through a conduit 340A to a liquid header 342A for supplying the evaporators 344A. A second refrigeration system, for example a low temperature system, employs a compressor 312 discharging refrigerant to a separate condenser 326B and receiver 3283 and thence through conduit 340B to a header 342B connectedto the low temperature evaporators 344B. Between the receivers and liquid headers of these conventional systems, a heat exchanger 390 of any convenient type is provided for cooling the liquid refrigerant to a predetermined level before it is conducted to the headers 342A and 342B. The cooling in heat exchanger 390 i is accomplished by an evaporator 391 having its suction connected to a separate compressor 381 for maintaining the desired temperature in heat exchanger 390.

' The discharge of compressor 381 is connected through another separate condenser 326C to a receiver 328C and thence through an expansion valve 392 to the evaporator 391. In this manner again it is contemplated by his invention that the temperature reduction in the liquid refrigerant supplied to the multiplicity of fixture ent. The compressor 381 operates at a highly efficient level in that evaporator 391 is maintained at this desired intermediate temperature. For example, in thecontext of the previously described systems, the compressor 381 and evaporator 391 together with their usual controls will serve to produce a liquid refrigerant temperature of approximately 50F as supplied to headers 342A and 3428. Although the pressure of the liquid refrigerant in headers 342A and 342B will not be reduced as was accomplished in the systems of FIGS.

1, 2 and 3, the temperature differential between the header and the evaporator is similar and therefore the quantity of flash gas that will be created is similarly minimized. The system of FIG. 4 is particularly advantageous when applied to either a previously installed system requiring additional capacity or in an overall system employing two or more separate refrigeration cycles (as illustrated) wherein different types of refrigerant are used in the separate systems due to the different advantageous characteristics of the refrigerants. In either situation the heat exchanger 390 and the separate refrigeration cycle including separate compressor 381 may be readily sized and installed to achieve the desired objectives. In actual practice, the capacity of an existing system of compressors can be increased by 40 to percent by the addition of a compressor 381 of merely 10 to 15 percent of the total capacities of the existing compressors, whereby fixtures may be readily added to the installation.

system of this invention in a simplified form comprising a single refrigeration system for operating a multiplicity of evaporators at a given temperature level. Numerals in the 400 series will be employed for identifying components similar to those appearing in the preceding Figures. Compressor 410 has its discharge 422 connected to an oil accumulator and separator 423 which in turn is connected through a standpipe 424 to a condenser 426 and thence to a receiver 428. Liquid refrigerant is supplied through a conduit 440 and a subcooler 490 to a liquid header 442 and thence to evaporators 444. A suction conduit 454 is connected from the evaporators 444 to the suction of compressor 410 to complete the refrigeration cycle. While only two evaporators 444 are illustrated it is contemplated and this system is adapted to accommodate a multiplicity of evaporators operating at this suction pressure level. The sub-cooler 490 has an evaporator coil 491 with refrigerant supplied through expansion valve 492 from conduit 440 and the suction from the coil is connected through conduit 480 to a separate compressor 481, the discharge of which is'connected by conduit 483 to the oil separator 423. It is to be noted that compressors 410 and 481 are provided with an oil return system of the type shown and described with respect to FIG. 1 employing valves 435 and level controls 436 for returning the oil from separator 423. Again it is contemplated by this invention that the liquid refrigerant temperature reduction by sub-cooler 490, as operated by compressor 481, will be of an extreme magnitude many times that which is normally accomplished by a sub cooler. The temperature reduction is performed at an efficient level in thatcompressor 481 operates with a relatively high suction pressure in the manner previously described with respect to the other systems. Most of the advantages and improvements and efficiencies are the same with this system aspreviously described. As an example of the improved efficiency accomplished by this invention as applied to a system of the type illustrated in FIG. 5, the addition of an appropriately sized compressor 481 and sub-cooler 490 to a single staged system using Refrigerant-502 operating at a -40F suction and l20F condensing temperature will increase the overall efficiency by 50 percent by reason of the two compressors producing approximately 69 percent more work although the separate compressor 481 has FIG. 5 illustrates still another modified form of the a horsepower requirement of only 16 percent of the system compressor 410.

Having fully described my invention in connection with selected embodiments and arrangements by way of examples, it is to be understood that my invention is not limited to such specific embodiments and arrangements as disclosed herein but rather is of the full scope of the appended claims.

I claim:

1. In a closed cycle refrigeration system for a multiplicity of refrigerated fixtures, comprising a like multiplicity of evaporator means associated with and cooling the fixtures, compressor means for compressing the evaporated refrigerant, condenser means for condensing the refrigerant to a liquid at a temperature substantially above room temperature, a receiver for maintaining a supply of liquid refrigerant for the variable demand of said multiplicity of evaporator means, a separate vessel forming a chamber for receiving the liquid refrigerant from said receiver, a pressure reducing valve between said receiver and said chamber, and means employing the suction of said compressor means at a relatively high pressure level connected to said chamber to, evaporate some refrigerant for reducing the temperature of all the liquid refrigerant in said chamber being supplied to said evaporator means to a temperature below both the condensing temperature and above the temperature maintained by said evapo rator means.

2. In a closed cycle refrigeration system for a multiplicity of refrigerated fixtures, comprising a like multiplicity of evaporator means associated with and cooling the fixtures, compressor means for compressing the evaporated refrigerant, condenser means for condensing the refrigerant to a liquid at a temperature substantially above room temperature, a receiver means for maintaining a supply of liquid refrigerant for the variable demand of said multiplicity of evaporator means including a chamber through which all of the com densed refrigerant passes, means employing the suction of said compressor means at a relatively high pressure level connected to said chamber to evaporate some refrigerant for reducing the temperature of all the liquid refrigerant in said chamber being supplied to said evaporator means to a temperature below both the condensing temperature and room temperature and above the temperature maintained by said evapoartor means, means provided for defrosting the evaporator means by passing hot gaseous refrigerant therethrough, and means for conducting the defrosting refrigerant from the evaporator means to said chamber for separating gaseous and liquid refrigerant and returning the liquid refrigerant to the refrigerating cycle.

3. In a closed cycle refrigeration system for a multiplicity of refrigerated fixtures, comprising a like multiplicity of evaporator means associated with and cooling the fixtures, compressor means for compressing the evaporated refrigerant, condenser means for condensing the refrigerant to a liquid at a temperature substantially above room temperature, a receiver for maintaining a supply of liquid refrigerant for the variable demand of said multiplicity of evaporator means, a heat exchanger through which the liquid refrigerant passes from said receiver to said evaporator means, and means comprising a completely separate closed cycle refrigeration system having a compressor, condenser, receiver and evaporator coil with the evaporator coil forming one separate portion of the heat exchanger, said separate compressor operating at a relatively high suction pressure level for reducing the temperature of all of the liquid refrigerant passing through the heat exchanger and being supplied to said system evaporator means to a temperature below both the condensing temperature and room temperature but above the temperature maintained by said evaporator means.

4. In a closed cycle refrigeration system for a multiplicity of refrigerated fixtures, comprising a like multiplicity of evaporator means associated with and cooling the fixtures, compressor means for compressing the evaporated refrigerant, condenser means for condensing the refrigerant to a liquid at a temperature substan tially above room temperature, a receiver for maintaining a supply of liquid refrigerant for the variable demand of said multiplicity of evaporator means, and means employing said compressor means both for reducing the pressure of the supply of liquid refrigerant to a constant value substantially below the head pressure produced by said compressor means and for reducing the temperature of all the liquid refrigerant being supplied to said evaporator means to a temperature below both the condensing temperature and room temperature and above the temperature maintained by said evaporator means.

5. The refrigeration system of claim 4 wherein the means for reducing the liquid refrigerant temperature includes a chamber through which all of the condensed refrigerant passes, and said suction of the compressor means is connected to said chamber for causing said evaporation of some refrigerant to cool the remaining liquid.

6. The refrigeration system of claim 4 wherein said temperature reduction of the liquid refrigerant is approximately one-half of the temperature differential between condensing temperature and evaporator temperature.

7. The refrigeration system of claim 4 wherein said compressor means includes a separate and independently operating compressor having its suction operating said means for reducing the liquid refrigerant temperature.

8. The refrigeration system of claim 7 wherein said means'for reducing the temperature and pressure of the liquid refrigerant includes the receiver with said separate compressor suction connected to the receiver, means for passing only liquid refrigerant from the condenser means to the receiver, and means for controlling the pressure in said receiver to said constant value.

9. In a closed cycle refrigeration system for a multiplicity of refrigerated fixtures, comprising a like multiplicity of evaporator means associated with and cooling the fixtures, compressor means for compressing the evaporated refrigerant, condenser means for condensing the refrigerant to a liquid at a temperature substantially above room temperature, a receiver for maintaining a supply of liquid refrigerant for the variable demand of said multiplicity of evaporator means, and means employing the suction of said compressor means at a relatively high pressure level to evaporate some refrigerant for reducing the temperature of all the liquid refrigerant being supplied to said evaporator means to a temperature below both the condensing temperature and room temperature and above the temperature maintained by said evaporator means, said the multiplicity of evaporator means being operated on at least two different temperature levels and the means for reducing the liquid refrigerant temperature including at least two separate chambers through which the condensed liquid refrigerant passes consecutively, said suction of the compressor means being connected to said chambers for causing evaporation of some refrigerant to cool the remaining liquid refrigerant to two different temperatures, the higher temperature being maintained in the first chamber with the liquid refrigerant therefrom being supplied to the higher temperature evaporator means and to the second chamber, and the colder liquid refrigerant from said second chamber being supplied to the remaining evaporator means.

10. The refrigeration system of claim 9 wherein the compressor means includes a separate and independently operating compressor having its suction connected to said first chamber.

11. The refrigeration system of claim 10 wherein said compressor means includes separate compressor operating the evaporator means at different temperature levels, and compressor operating said higher temperature evaporator means has its suction also connected to said second chamber.

12. The refrigeration system of claim 10 wherein the compressor means includes a second separate and independently operating compressor having its suction connected to said second chamber. 1

13. The refrigeration system of claim 12 wherein a third chamber and third separate compressor operating same are provided and connected downstream of said second chamber for providing even colder liquid refrigerant to the evaporator means operating at the coldest temperature.

1,4. In a refrigeration system having compressor means, condenser-receiver means and evaporator means with a substantial temperature range differential between the high temperature of the liquid refrigerant resulting in said condenser-receiver means and the low refrigerant temperature maintained in the evaporator means, the improvement comprising, a separate and independent compressor means operating at a relatively high suction pressure for evaporating refrigerant at a temperature intermediate such temperature range differential, and means employing the suction of said separate compressor means in association with the high temperature liquid refrigerant for reducing the temperature and pressure of that refrigerant to substantially said intermediate temperature and to a substantially constant pressure before supplying same to the evaporator means.

15. In a refrigeration system the combination of a first compressor means, a condenser, a receiver, and a plurality of evaporator means all connected in a closed cycle with the liquid refrigerant resulting in said condenser normally having a high temperature substantially above room temperature and said evaporator emans operating at temperatures near or below freezing, valve means connected between said condenser and said receiver for permitting only liquid refrigerant to flow to said receiver, a separate continuously operating compressor means having the suction connected to said receiver for producing a relatively high suction pressure and refrigerant evaporation-temperature for reducing the temperature and pressure of the liquid refrigerant-in said receiver to below room temperature and to a substantially constant pressure, and said separate compressor means having its discharge connected to said condenser for returning the refrigerant to said closed cycle. 7 

1. In a closed cycle refrigeration system for a multiplicity of refrigerated fixtures, comprising a like multiplicity of evaporator means associated with and cooling the fixtures, compressor means for compressing the evaporated refrigerant, condenser means for condensing the refrigerant to a liquid at a temperature substantially above room temperature, a receiver for maintaining a supply of liquid refrigerant for the variable demand of said multiplicity of evaporator means, a separate vessel forming a chamber for receiving the liquid refrigerant from said receiver, a pressure reducing valve between said receiver and said chamber, and means employing the suction of said compressor means at a relatively high pressure level connected to said chamber to evaporate some refrigerant for reducing the temperature of all the liquid refrigerant in said chamber being supplied to said evaporator means to a temperature below both the condensing temperature and above the temperature maintained by said evaporator means.
 2. In a closed cycle refrigeration system for a multiplicity of refrigerated fixtures, comprising a like multiplicity of evaporator means associated with and cooling the fixtures, compressor means for compressing the evaporated refrigerant, condenser means for condensing the refrigerant to a liquid at a temperature substantially above room temperature, a receIver means for maintaining a supply of liquid refrigerant for the variable demand of said multiplicity of evaporator means including a chamber through which all of the condensed refrigerant passes, means employing the suction of said compressor means at a relatively high pressure level connected to said chamber to evaporate some refrigerant for reducing the temperature of all the liquid refrigerant in said chamber being supplied to said evaporator means to a temperature below both the condensing temperature and room temperature and above the temperature maintained by said evaporator means, means provided for defrosting the evaporator means by passing hot gaseous refrigerant therethrough, and means for conducting the defrosting refrigerant from the evaporator means to said chamber for separating gaseous and liquid refrigerant and returning the liquid refrigerant to the refrigerating cycle.
 3. In a closed cycle refrigeration system for a multiplicity of refrigerated fixtures, comprising a like multiplicity of evaporator means associated with and cooling the fixtures, compressor means for compressing the evaporated refrigerant, condenser means for condensing the refrigerant to a liquid at a temperature substantially above room temperature, a receiver for maintaining a supply of liquid refrigerant for the variable demand of said multiplicity of evaporator means, a heat exchanger through which the liquid refrigerant passes from said receiver to said evaporator means, and means comprising a completely separate closed cycle refrigeration system having a compressor, condenser, receiver and evaporator coil with the evaporator coil forming one separate portion of the heat exchanger, said separate compressor operating at a relatively high suction pressure level for reducing the temperature of all of the liquid refrigerant passing through the heat exchanger and being supplied to said system evaporator means to a temperature below both the condensing temperature and room temperature but above the temperature maintained by said evaporator means.
 4. In a closed cycle refrigeration system for a multiplicity of refrigerated fixtures, comprising a like multiplicity of evaporator means associated with and cooling the fixtures, compressor means for compressing the evaporated refrigerant, condenser means for condensing the refrigerant to a liquid at a temperature substantially above room temperature, a receiver for maintaining a supply of liquid refrigerant for the variable demand of said multiplicity of evaporator means, and means employing said compressor means both for reducing the pressure of the supply of liquid refrigerant to a constant value substantially below the head pressure produced by said compressor means and for reducing the temperature of all the liquid refrigerant being supplied to said evaporator means to a temperature below both the condensing temperature and room temperature and above the temperature maintained by said evaporator means.
 5. The refrigeration system of claim 4 wherein the means for reducing the liquid refrigerant temperature includes a chamber through which all of the condensed refrigerant passes, and said suction of the compressor means is connected to said chamber for causing said evaporation of some refrigerant to cool the remaining liquid.
 6. The refrigeration system of claim 4 wherein said temperature reduction of the liquid refrigerant is approximately one-half of the temperature differential between condensing temperature and evaporator temperature.
 7. The refrigeration system of claim 4 wherein said compressor means includes a separate and independently operating compressor having its suction operating said means for reducing the liquid refrigerant temperature.
 8. The refrigeration system of claim 7 wherein said means for reducing the temperature and pressure of the liquid refrigerant includes the receiver with said separate compressor suction connected to the receiver, means for passing only liquid refrigerant from the condenser means to the receiver, and means for controlling the pressure in said receiver to said constant value.
 9. In a closed cycle refrigeration system for a multiplicity of refrigerated fixtures, comprising a like multiplicity of evaporator means associated with and cooling the fixtures, compressor means for compressing the evaporated refrigerant, condenser means for condensing the refrigerant to a liquid at a temperature substantially above room temperature, a receiver for maintaining a supply of liquid refrigerant for the variable demand of said multiplicity of evaporator means, and means employing the suction of said compressor means at a relatively high pressure level to evaporate some refrigerant for reducing the temperature of all the liquid refrigerant being supplied to said evaporator means to a temperature below both the condensing temperature and room temperature and above the temperature maintained by said evaporator means, said the multiplicity of evaporator means being operated on at least two different temperature levels and the means for reducing the liquid refrigerant temperature including at least two separate chambers through which the condensed liquid refrigerant passes consecutively, said suction of the compressor means being connected to said chambers for causing evaporation of some refrigerant to cool the remaining liquid refrigerant to two different temperatures, the higher temperature being maintained in the first chamber with the liquid refrigerant therefrom being supplied to the higher temperature evaporator means and to the second chamber, and the colder liquid refrigerant from said second chamber being supplied to the remaining evaporator means.
 10. The refrigeration system of claim 9 wherein the compressor means includes a separate and independently operating compressor having its suction connected to said first chamber.
 11. The refrigeration system of claim 10 wherein said compressor means includes separate compressor operating the evaporator means at different temperature levels, and compressor operating said higher temperature evaporator means has its suction also connected to said second chamber.
 12. The refrigeration system of claim 10 wherein the compressor means includes a second separate and independently operating compressor having its suction connected to said second chamber.
 13. The refrigeration system of claim 12 wherein a third chamber and third separate compressor operating same are provided and connected downstream of said second chamber for providing even colder liquid refrigerant to the evaporator means operating at the coldest temperature.
 14. In a refrigeration system having compressor means, condenser-receiver means and evaporator means with a substantial temperature range differential between the high temperature of the liquid refrigerant resulting in said condenser-receiver means and the low refrigerant temperature maintained in the evaporator means, the improvement comprising, a separate and independent compressor means operating at a relatively high suction pressure for evaporating refrigerant at a temperature intermediate such temperature range differential, and means employing the suction of said separate compressor means in association with the high temperature liquid refrigerant for reducing the temperature and pressure of that refrigerant to substantially said intermediate temperature and to a substantially constant pressure before supplying same to the evaporator means.
 15. In a refrigeration system the combination of a first compressor means, a condenser, a receiver, and a plurality of evaporator means all connected in a closed cycle with the liquid refrigerant resulting in said condenser normally having a high temperature substantially above room temperature and said evaporator means operating at temperatures near or below freezing, valve means connected between said condenser and said receiver for permitting only liquid refrigerant to flow to said receiver, a separate continuously operating compressor means haVing the suction connected to said receiver for producing a relatively high suction pressure and refrigerant evaporation temperature for reducing the temperature and pressure of the liquid refrigerant in said receiver to below room temperature and to a substantially constant pressure, and said separate compressor means having its discharge connected to said condenser for returning the refrigerant to said closed cycle. 